System and method for measuring fluid properties using magnetic field techniques via magnetic tracer

ABSTRACT

A method and apparatus for determining a property of a fluid in a vessel. The method uses magnetic tracer particles and an externally applied magnetic field which orients the particles. When the fluid moves, it changes the orientation of the tracer particles, thus changing the magnetic fields. These changes are detected by external magnetic field sensors. By using mathematical models, the property of the fluid in the vessel is determined from the detected magnetic field. In this manner, fluid vorticity, velocity, strain and stress may be estimated.

GOVERNMENT LICENSE RIGHTS

This invention was made with Government support under Contract No.DE-NA0003525 awarded by the United States Department of Energy/NationalNuclear Security Administration. The U.S. Government has certain rightsin the invention.

BACKGROUND INFORMATION 1. Field

The present disclosure relates generally to systems and methods formeasuring fluid properties using magnetic field techniques via tracerparticles. This includes techniques for measuring fluid properties suchas vorticity, velocity, strain and stress. Additional properties such asmotion, rotation, vibration, temperature, and electrical-currentproperties can also be measured. Illustrative embodiments allowmeasurements to be made through optically opaque environments atrelatively high speeds. More particularly, illustrative embodiments aredirected to a system and method for remotely and directly measuringthese properties.

2. Background

Vorticity is a measure of local fluid rotation commonly utilized tounderstand and visualize flow structures from viscous to inviscid toturbulent flows. Vorticity may be used to understand circulation andlift, viscous stresses on a fluid volume, and boundary layer effects.With a clear understanding of boundary conditions, vorticity may be usedto infer velocity profiles throughout a flow.

Conventional methods of measuring vorticity first measure velocityfields and then calculate vorticity indirectly. These methods includeparticle image velocimetry (PIV), magnetic resonance velocimetry, andX-ray PIV.

Methods previously developed for measuring vorticity directly userotating-vane meters, torque sensors, laser Doppler shift, opticalparticle cluster tracking, and optical particle orientation tracking.Most of these methods, however, require an optically transparent accessport or an optically transparent flow that may be transparent to anywavelengths including visible, infrared, ultraviolet, microwave, radar,and x-ray. Magnetic resonance and ultrasound techniques are inherentlyspeed limited.

Therefore, it may be desirable to have a method and apparatus that takeinto account at least some of the issues discussed above, as well asother possible issues.

SUMMARY

Illustrative embodiments provide a method of determining a property of afluid in a vessel. A detected magnetic field is measured from outside ofthe vessel. The detected magnetic field is generated by magneticparticles in the fluid. The property of the fluid in the vessel isdetermined from the detected magnetic field.

Illustrative embodiments also provide a method of determining a propertyof a fluid in a vessel. An applied magnetic field is applied to thefluid in the vessel from outside of the vessel to rotationally alignmagnetic dipole particles in the fluid. The applying of the appliedmagnetic field to the fluid in the vessel is stopped when the magneticdipole particles in the fluid are rotationally aligned. After stoppingapplying the applied magnetic field, a magnetic field is detectedoutside of the vessel. The detected magnetic field is generated by themagnetic dipole particles in the fluid. The property of the fluid in thevessel is determined from the detected magnetic field. A graphicalrepresentation of the property of the fluid in the vessel is displayed.

Illustrative embodiments also provide an apparatus comprising a magneticfield generator, a magnetic field generator controller, a magnetic fieldsensor, a fluid flow calculator, and a display generator. The magneticfield generator controller is configured to control the magnetic fieldgenerator to apply an applied magnetic field to a fluid in a vessel fromoutside of the vessel to rotationally align magnetic dipole particles inthe fluid and to stop applying the applied magnetic field to the fluidin the vessel when the magnetic dipole particles in the fluid arerotationally aligned. The magnetic field sensor is configured to detecta detected magnetic field outside of the vessel, wherein the detectedmagnetic field is generated by the magnetic dipole particles in thefluid after applying the applied magnetic field to the fluid in thevessel is stopped. The fluid flow calculator is configured to determinea flow of the fluid in the vessel from the detected magnetic field. Thedisplay generator is configured to generate a graphical representationof the flow of fluid in the vessel.

The features and functions may be achieved independently in variousembodiments of the present disclosure or may be combined in yet otherembodiments in which further details may be seen with reference to thefollowing description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the illustrativeembodiments are set forth in the appended claims. The illustrativeembodiments, however, as well as a preferred mode of use, furtherobjectives and features thereof, will best be understood by reference tothe following detailed description of an illustrative embodiment of thepresent disclosure when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is an illustration of a block diagram of a material flow sensingsystem for determining properties of a fluid in a vessel in accordancewith an illustrative embodiment;

FIG. 2 is an illustration of tracer magnetic particles in a fluid at atime when a magnetic field generator is generating an applied magneticfield in accordance with an illustrative embodiment;

FIG. 3 is an illustration of tracer magnetic particles in a fluid at atime after the magnetic field generator has stopped generating anapplied magnetic field and the tracer magnetic particles have moved dueto fluid properties in accordance with an illustrative embodiment;

FIG. 4 is an illustration of a flowchart of a process for determining aproperty of a fluid in a vessel in accordance with an illustrativeembodiment;

FIG. 5 is an illustration of a flowchart of a process for determining aflow of fluid in a vessel in accordance with an illustrative embodiment;and

FIG. 6 is an illustration of a block diagram of a data processing systemin accordance with an illustrative embodiment.

DETAILED DESCRIPTION

The illustrative embodiments recognize and take into account one or moredifferent considerations. For example, the illustrative embodimentsrecognize and take into account that many applications, including manynational-security applications, may have a need for flow, temperature,vibration and electrical-current diagnostics that can be applied tohigh-temperature high-pressure (HTHP) opaque vessels and materials.Examples include liquefaction of organic materials, porous-media flows,thermal decomposition of explosives, high-voltage breakdown, shock wavepropagation, and heat-exchanger optimization. Quantitative measurementsof these phenomena within sealed vessels under HTHP conditions areparticularly challenging, as optical access is often infeasible. Forassured safety, characterization and understanding of fluid temperature,vibration, and electrical behavior under HTHP conditions is desired.

Illustrative embodiments provide for determining characteristics ofliquid flow in opaque vessels using magnetic-field diagnostics. Inaccordance with an example illustrative embodiment, the fluid may beseeded with magnetic particles, a time-varying field is applied torotationally induce dipole alignment within well-defined regions, andthen the flow-induced particle-driven magnetic time-varying fieldoutside the vessel is observed using magnetometers. The magnetic fieldobservations are inverted to provide a three-dimensional, time varyingimage of fluid motions.

Turning to FIG. 1, an illustration of a block diagram of a material flowsensing system for determining properties of a fluid in a vessel isdepicted in accordance with an illustrative embodiment. Material flowsensing system 100 may be configured to determine one or more properties102 of fluid 104 in vessel 106.

Vessel 106 may comprise any appropriate container for containing anyappropriate fluid 104. For example, without limitation, vessel 106 maybe optically opaque vessel 108 that is magnetically transparent.Magnetically transparent vessel 109 is transparent to magnetic fields.

Fluid 104 may comprise any appropriate fluid. For example, withoutlimitation, fluid 104 may be optically opaque fluid 110 that ismagnetically transparent. Magnetically transparent fluid 111 istransparent to magnetic fields.

In accordance with an illustrative embodiment, fluid 104 has magneticparticles 112 therein. For example, without limitation, magneticparticles 112 may be magnetic dipole particles 114.

Magnetic flow sensing system 100 may comprise magnetic field generator116, magnetic field sensors 118, and computer 120.

Magnetic field generator 116 may be configured to generated appliedmagnetic field 122 that is applied to fluid 104 in vessel 106. Forexample, without limitation, magnetic field generator 116 may beimplemented using Helmholtz coils 124.

Magnetic field sensors 118 may be configured to detect detected magneticfield 126, wherein detected magnetic field 126 is generated by magneticparticles 112 in fluid 104. For example, without limitation, magneticfield sensors 118 may comprise magnetometers 128 or giantmagneto-resistive sensors, GMR. Information regarding detected magneticfield 126 detected by magnetic field sensors 118 may be provided asmagnetic field measurements 130 to computer 120.

Computer 120 may be implemented using any appropriate informationprocessing system. Computer 120 may be configured using any appropriatehardware or hardware in combination with software to implement magneticfield generator controller 132, fluid property calculator 134, displaygenerator 136, and display 138.

Fluid property calculator 134 may be configured to determine properties102 of fluid 104 in vessel 106 from magnetic field measurements 130provided by magnetic field sensors 118. For example, without limitation,fluid property calculator 134 may comprise one or more of fluid flowcalculator 140, fluid temperature calculator 142, and fluid stress andstrain calculator 144.

Fluid flow calculator 140 may be configured to determine flow 146 offluid 104 in vessel 106 from magnetic field measurements 130. Forexample, without limitation, fluid flow calculator 140 may be configuredto determine vorticity 148, velocity 149, or other characteristics offlow 146 of fluid 104 in vessel 106. For example, without limitation,fluid flow calculator 140 may be configured to determine flow 146 offluid 104 in vessel 106 from magnetic field measurements 130 using fluidfield model 154 and particle field model 156.

An example of using fluid field model 154 and particle field model 156to determine flow 146 of fluid 104 in vessel 106 will now be describedin more detail. This particular example is for a fluid between twoconcentric semi-infinite cylinders, wherein the outer cylinder is fixedand the inner cylinder is spinning. Illustrative embodiments are notlimited to the specific example described herein.

Small magnetic tracer particles 112 can be approximated as dipoles withmagnetic fields that can be measured at some distance. The followingmodel for the magnetic field of magnetic dipole tracer particles 114 isan example of one implementation of particle field model 156. Start bydefining magnetic field sensors i=1, . . . , I located at positions{right arrow over (x)}_(i) ^(s)=({right arrow over (x)}_(ix) ^(s),{rightarrow over (x)}_(iy) ^(s),{right arrow over (x)}_(iz) ^(s))^(T) and anensemble of permanent magnetic field particles i=1, . . . , J located atpositions {right arrow over (x)}_(j) ^(p)=({right arrow over (x)}_(jx)^(p),{right arrow over (x)}_(jy) ^(p),{right arrow over (x)}_(jz)^(p))^(T) with normalized orientations {right arrow over(m)}_(j)=({right arrow over (m)}_(jx),{right arrow over (m)}_(jy),{rightarrow over (m)}_(jz))^(T). The magnetic field from the residualinduction of a single particle on a single sensor can be approximated as

${\overset{\rightarrow}{B}}_{ij} = {B_{j}\left( {\frac{3\left( {{\overset{\rightarrow}{m}}_{j} \cdot {\overset{\rightarrow}{x}}_{ij}} \right)}{R_{ij}^{5}} - \frac{{\overset{\rightarrow}{m}}_{j}}{R_{ij}^{3}}} \right)}$where {right arrow over (x)}i_(j)={right arrow over (x)}_(i) ^(s)−{rightarrow over (x)}_(j) ^(p) is the relative position, R_(ij)=∥{right arrowover (x)}_(i) ^(s)−{right arrow over (x)}_(k) ^(p)∥ is the distance. Themagnetic field at room temperature is

$B_{j} \approx {\frac{\mu_{0}}{4\;\pi}\mu_{r}M_{0}V_{j}}$where M₀ is the uniform magnetization, μ_(r) is the relativepermeability, μ₀ is the magnetic vacuum permeability, and V_(j) is thevolume of the magnet. The total contribution of J magnets on sensor i is{right arrow over (B)}_(i)=Σ{right arrow over (B)}_(ij)+{right arrowover (C)}_(i) where {right arrow over (C)}_(i) are offset constants fromfixed external magnetic fields like the magnetic field of the earth.

In a uniformly seeded flow, the number of particles vastly outnumbersthe number of sensor readings. Hence, the full volume model can bebroken up into sub-volumes over which vorticity can be estimated using anonlinear least squares formulation

${\min\limits_{{\overset{\rightarrow}{\theta}}_{B}}{f\left( {\overset{\rightarrow}{\theta}}_{B} \right)}},{{f\left( {\overset{\rightarrow}{\theta}}_{B} \right)} = {{\overset{\rightarrow}{Y} - {\overset{\rightarrow}{B}\left( {\overset{\rightarrow}{\theta}}_{B} \right)}}}},$where {right arrow over (Y)} is the offset-compensated magnetic-fieldmeasurements. For a uniformly seeded flow, knowledge of the location ofany individual particle is not needed but the vorticity or rotation ofthe flow can estimated. Therefore, the nonlinear least squaresformulation searches for the bulk rotation of the particles or {rightarrow over (θ)}_(B) from the ensemble orientations {right arrow over(m)}_(j) of all the particles.

A simple illustration of one possible embodiment of this techniquemeasures the fluid vorticity inside a Taylor-Couette flow. Thistwo-dimensional flow is enclosed by a cylindrical vessel and is drivenby a cylindrical rod placed in the center of the vessel. As the rodrotates, it moves the fluid in the vessel due to viscous forces. Theequations describing the vorticity and velocity fields can be derivedfrom the Navier-Stokes equations assuming the flow is isentropic, notpressure driven and steady. The equation simplifies to ∇²v=0. With noradial or axial velocity, the differential equation can be written as

${{\frac{1}{r}\frac{\partial}{\partial r}\left( {r\frac{\partial v_{\theta}}{\partial r}} \right)} - \frac{v_{\theta}}{r^{2}}} = 0.$For a fixed outer cylinder and spinning inner cylinder with angularvelocity Ω, the boundary conditions are v_(θ)(R₂)=0 and v_(θ)(R₁)=R₁Ωwith the radius of the vessel defined as R₂ and the radius of therotating rod defined as R₁. Using a solution of the form

${v_{\theta} = {{Ar} + \frac{B}{r}}},$the angular velocity as a function of radius is

${v_{\theta}(r)} = {\frac{\Omega\; R_{1}^{2}}{R_{2}^{2} - R_{1}^{2}}{\left( {\frac{R_{2}^{2}}{r} - r} \right).}}$The vorticity of the flow is defined as

${\omega = {{\nabla{\times v}} = {{\frac{1}{r}\frac{\partial\left( {rv}_{\theta} \right)}{\partial r}} = {\frac{{- 2}R_{1}^{2}}{R_{2}^{2} - R_{1}^{2}}\Omega}}}},$which in this case is constant throughout the flow and rotating in theopposite direction with respect to the rotating cylindrical rod.

When using very small spherical particles with respect to thecharacteristic length of the flow, the rotational rate of the particlesis ω_(p)=ω/2 corresponding to the shear rate of the flow. The magneticfield measurement produces estimates of the net rotation of the fieldθ_(B) such that

$\frac{d\;\theta_{B}}{dt} = {\omega_{p}.}$Thus, in steady-state, the estimated angular rotation of the magneticfield should be

${\theta_{B} = {\frac{- R_{1}^{2}}{R_{2}^{2} - R_{1}^{2}}\theta_{R\; 1}}},$where θ_(R1) is the angle of the inner cylindrical rod. Thus, themeasured solution θ_(B) can be validated with known rod rotation θ_(R1)and can also be used to estimate fluid vorticity ω and fluid velocityv_(θ)(r) using the known boundary conditions. The strain rate tensorϵ=½(∇v+∇v^(T)) and viscous stress tensor τ=μ(∇v+∇v^(T)) can also becalculated for this flow.

Several scaling laws are taken into account to apply this technique.First, the magnetic particles should settle out of the flow due togravity or buoyancy on timescales slower than the timescale of themeasurement. Second, the magnetic particle must have small translationand rotational Stokes numbers in order for the tracer particles tofollow the flow. In order to initially align the particles, the magnetictorque of the externally applied field T_(m) should be stronger than thefluid drag T_(d) and Brownian motion T_(b) forces. In order for themagnetic particles to be used as tracer particles after the externallyapplied field is turned off, the fluid drag must dominate over theresidual magnetic torques T_(r). This produces the following conditionT_(m)>T_(d)>T_(r)>T_(b).

In an exemplary experiment, silicone oils (Dow Corning 200 fluid) andmicroscopic approximately 5 micrometer Alnico (iron alloy containingaluminum nickel and cobalt) magnetic particles were used. The particleswere seeded at a 0.1% by volume into the fluid to minimize disturbancesto the flow. The particles were placed in a fluid cell with a diameterof 25.4 mm. An aluminum rod of diameter 6.35 mm was used as the internalrotating rod. The rod was attached to a rotational motor with a bearingstructure and a shaft coupling. The motor (Animatics SM23165D) wasplaced outside two-axis Helmholtz coils (Lakeshore MH-2X-10) that weredriven by two amplifiers (Kepco BOP-50-8ML-4886). To avoid saturatingthe sensors, the Helmholtz coils were driven up to 6 Gauss. Three-axismagnetic field sensors (Honeywell HMC1053) on custom circuit boards wereplaced close to the sides of the fluid cell. The sensors interfaced witha 16-bit PXI-6255 data acquisition card and a NI-PXIe-1073 chassis.Aluminum and plastic components were used to minimize field steeringeffects. LabVIEW was used for controlling the Helmholtz coils,implementing calibrations, and acquiring experimental data. MATLAB wasused to convert sensor measurements into fluid property estimates.

Fluid temperature calculator 142 may be configured to determinetemperature 150 of fluid 104 in vessel 106 from magnetic fieldmeasurements 130.

Fluid stress and strain calculator 144 may be configured to determinestress and strain 152 of fluid 104 in vessel 106 from magnetic fieldmeasurements 130.

The illustration of material flow sensing system 100 in FIG. 1 is notmeant to imply physical or architectural limitations to the manner inwhich illustrative embodiments may be implemented. Other components, inaddition to or in place of the ones illustrated, may be used. Somecomponents may be optional. Also, the blocks are presented to illustratesome functional components. One or more of these blocks may be combined,divided, or combined and divided into different blocks when implementedin an illustrative embodiment.

Turing to FIG. 2, an illustration of tracer magnetic particles in afluid at a time when a magnetic field generator is generating an appliedmagnetic field is depicted in accordance with an illustrativeembodiment. Vessel 200 containing fluid 202 may be an example of across-section of one implementation of vessel 106 containing fluid 104in FIG. 1.

Magnetic dipole particles are distributed in fluid 202 and are moved bythe movement of fluid 202 in vessel 200. For example, magnetic dipoleparticle 204 is moved in fluid 202 along a velocity vector indicated byarrow 206 and is rotated in the direction of arrow 208 by localvorticity in fluid 202.

A magnetic field in the direction indicated by arrow 210 is applied tovessel 200. As shown, the applied magnetic field aligns the magneticdipole particles in fluid 202 to the same orientation in the xdirection. At time t=0, the application of the applied magnetic field tovessel 200 is stopped.

Turning to FIG. 3, an illustration of tracer magnetic particles in afluid at a time after the magnetic field generator has stoppedgenerating an applied magnetic field and the tracer magnetic particleshave moved due to fluid properties is depicted in accordance with anillustrative embodiment. FIG. 3 shows vessel 200 containing fluid 202 ofFIG. 2 at a time t>0.

As shown, at a time t>0 the magnetic dipole particles have moved inposition and rotated due to flow of fluid 202 in vessel. At this time,the magnetic dipole particles produce a bulk magnetic field in thedirection of arrow 300. As described herein, in accordance with anillustrative embodiment, the magnetic field generated by the magneticdipole particles at time t>0 may be detected from outside of vessel 200and used to determine properties of fluid 202 in vessel 200, such asvorticity, velocity, stress and strain.

Turning to FIG. 4, an illustration of a flowchart of a process fordetermining a property of a fluid in a vessel is depicted in accordancewith an illustrative embodiment. Process 400 may be implemented inmaterial flow sensing system 100 in FIG. 1.

Process 400 may begin with detecting a magnetic field outside of avessel, wherein the detected magnetic field is generated by magneticparticles in a fluid in the vessel (operation 402). A property of thefluid in the vessel may then be determined from the detected magneticfield (operation 406), with the process terminating or repeatingthereafter.

Turning to FIG. 5, an illustration of a flowchart of a process fordetermining a flow of fluid in a vessel is depicted in accordance withan illustrative embodiment. Process 500 may be implemented in materialflow sensing system 100 in FIG. 1. Process 500 may be a more specificexample of process 400 in FIG. 4.

Process 500 may begin with placing magnetic dipole particles in a fluidin a vessel (operation 502). An applied magnetic field may then beapplied to the fluid in the vessel to rotationally align the magneticdipole particles (operation 504). Applying of the applied magnetic fieldmay be stopped when the magnetic dipole particles are rotationallyaligned (operation 506). A detected magnetic field may then be detectedoutside the vessel, wherein the detected magnetic field is generated bythe magnetic dipole particles after applying the applied magnetic fieldis stopped (operation 508). A flow of fluid in the vessel may then bedetermined from the detected magnetic field (operation 510). A graphicalrepresentation of the flow of fluid in the vessel may then be generatedand displayed (operation 512), with the process terminating or repeatingfrom operation 504 thereafter.

Turning to FIG. 6, an illustration of a block diagram of a dataprocessing system is depicted in accordance with an illustrativeembodiment. Data processing system 600 is an example of one possibleimplementation of computer 120 in material flow sensing system 100 inFIG. 1.

In this illustrative example, data processing system 600 includescommunications fabric 602.

Communications fabric 602 provides communications between processor unit604, memory 606, persistent storage 608, communications unit 610,input/output (I/O) unit 612, and display 614. Memory 606, persistentstorage 608, communications unit 610, input/output (I/O) unit 612, anddisplay 614 are examples of resources accessible by processor unit 604via communications fabric 602.

Processor unit 604 serves to run instructions for software that may beloaded into memory 606. Processor unit 604 may be a number ofprocessors, a multi-processor core, or some other type of processor,depending on the particular implementation. Further, processor unit 604may be implemented using a number of heterogeneous processor systems inwhich a main processor is present with secondary processors on a singlechip. As another illustrative example, processor unit 604 may be asymmetric multi-processor system containing multiple processors of thesame type.

Memory 606 and persistent storage 608 are examples of storage devices616. A storage device is any piece of hardware that is capable ofstoring information, such as, for example, without limitation, data,program code in functional form, and other suitable information eitheron a temporary basis or a permanent basis. Storage devices 616 also maybe referred to as computer readable storage devices in these examples.Memory 606, in these examples, may be, for example, a random accessmemory or any other suitable volatile or non-volatile storage device.Persistent storage 608 may take various forms, depending on theparticular implementation.

For example, persistent storage 608 may contain one or more componentsor devices. For example, persistent storage 608 may be a hard drive, aflash memory, a rewritable optical disk, a rewritable magnetic tape, orsome combination of the above. The media used by persistent storage 608also may be removable. For example, a removable hard drive may be usedfor persistent storage 608.

Communications unit 610, in these examples, provides for communicationswith other data processing systems or devices. In these examples,communications unit 610 is a network interface card. Communications unit610 may provide communications through the use of either or bothphysical and wireless communications links.

Input/output (I/O) unit 612 allows for input and output of data withother devices that may be connected to data processing system 600. Forexample, input/output (I/O) unit 612 may provide a connection for userinput through a keyboard, a mouse, and/or some other suitable inputdevice. Further, input/output (I/O) unit 612 may send output to aprinter. Display 614 provides a mechanism to display information to auser.

Instructions for the operating system, applications, and/or programs maybe located in storage devices 616, which are in communication withprocessor unit 604 through communications fabric 602. In theseillustrative examples, the instructions are in a functional form onpersistent storage 608. These instructions may be loaded into memory 606for execution by processor unit 604. The processes of the differentembodiments may be performed by processor unit 604 usingcomputer-implemented instructions, which may be located in a memory,such as memory 606.

These instructions are referred to as program instructions, programcode, computer usable program code, or computer readable program codethat may be read and executed by a processor in processor unit 604. Theprogram code in the different embodiments may be embodied on differentphysical or computer readable storage media, such as memory 606 orpersistent storage 608.

Program code 618 is located in a functional form on computer readablemedia 620 that is selectively removable and may be loaded onto ortransferred to data processing system 600 for execution by processorunit 604. Program code 618 and computer readable media 620 form computerprogram product 622 in these examples. In one example, computer readablemedia 620 may be computer readable storage media 624 or computerreadable signal media 626.

Computer readable storage media 624 may include, for example, an opticalor magnetic disk that is inserted or placed into a drive or other devicethat is part of persistent storage 608 for transfer onto a storagedevice, such as a hard drive, that is part of persistent storage 608.Computer readable storage media 624 also may take the form of apersistent storage, such as a hard drive, a thumb drive, or a flashmemory, that is connected to data processing system 600. In someinstances, computer readable storage media 624 may not be removable fromdata processing system 600.

In these examples, computer readable storage media 624 is a physical ortangible storage device used to store program code 618 rather than amedium that propagates or transmits program code 618. Computer readablestorage media 624 is also referred to as a computer readable tangiblestorage device or a computer readable physical storage device. In otherwords, computer readable storage media 624 is a media that can betouched by a person.

Alternatively, program code 618 may be transferred to data processingsystem 600 using computer readable signal media 626. Computer readablesignal media 626 may be, for example, a propagated data signalcontaining program code 618. For example, computer readable signal media626 may be an electromagnetic signal, an optical signal, and/or anyother suitable type of signal. These signals may be transmitted overcommunications links, such as wireless communications links, opticalfiber cable, coaxial cable, a wire, and/or any other suitable type ofcommunications link. In other words, the communications link and/or theconnection may be physical or wireless in the illustrative examples.

In some illustrative embodiments, program code 618 may be downloadedover a network to persistent storage 608 from another device or dataprocessing system through computer readable signal media 626 for usewithin data processing system 600. For instance, program code stored ina computer readable storage medium in a server data processing systemmay be downloaded over a network from the server to data processingsystem 600. The data processing system providing program code 618 may bea server computer, a client computer, or some other device capable ofstoring and transmitting program code 618.

The different components illustrated for data processing system 600 arenot meant to provide architectural limitations to the manner in whichdifferent embodiments may be implemented. The different illustrativeembodiments may be implemented in a data processing system includingcomponents in addition to and/or in place of those illustrated for dataprocessing system 600. Other components shown in FIG. 6 can be variedfrom the illustrative examples shown. The different embodiments may beimplemented using any hardware device or system capable of runningprogram code. As one example, data processing system 600 may includeorganic components integrated with inorganic components and/or may becomprised entirely of organic components excluding a human being. Forexample, a storage device may be comprised of an organic semiconductor.

In another illustrative example, processor unit 604 may take the form ofa hardware unit that has circuits that are manufactured or configuredfor a particular use. This type of hardware may perform operationswithout needing program code to be loaded into a memory from a storagedevice to be configured to perform the operations.

For example, when processor unit 604 takes the form of a hardware unit,processor unit 604 may be a circuit system, an application specificintegrated circuit (ASIC), a programmable logic device, or some othersuitable type of hardware configured to perform a number of operations.With a programmable logic device, the device is configured to performthe number of operations. The device may be reconfigured at a later timeor may be permanently configured to perform the number of operations.Examples of programmable logic devices include, for example, aprogrammable logic array, a programmable array logic, a fieldprogrammable logic array, a field programmable gate array, and othersuitable hardware devices. With this type of implementation, programcode 618 may be omitted, because the processes for the differentembodiments are implemented in a hardware unit.

In still another illustrative example, processor unit 604 may beimplemented using a combination of processors found in computers andhardware units. Processor unit 604 may have a number of hardware unitsand a number of processors that are configured to run program code 618.With this depicted example, some of the processes may be implemented inthe number of hardware units, while other processes may be implementedin the number of processors.

In another example, a bus system may be used to implement communicationsfabric 602 and may be comprised of one or more buses, such as a systembus or an input/output bus. Of course, the bus system may be implementedusing any suitable type of architecture that provides for a transfer ofdata between different components or devices attached to the bus system.

Additionally, communications unit 610 may include a number of devicesthat transmit data, receive data, or both transmit and receive data.Communications unit 610 may be, for example, a modem or a networkadapter, two network adapters, or some combination thereof. Further, amemory may be, for example, memory 606, or a cache, such as that foundin an interface and memory controller hub that may be present incommunications fabric 602.

The flowcharts and block diagrams described herein illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousillustrative embodiments. In this regard, each block in the flowchartsor block diagrams may represent a module, segment, or portion of code,which comprises one or more executable instructions for implementing thespecified logical function or functions. It should also be noted that,in some alternative implementations, the functions noted in a block mayoccur out of the order noted in the figures. For example, the functionsof two blocks shown in succession may be executed substantiallyconcurrently, or the functions of the blocks may sometimes be executedin the reverse order, depending upon the functionality involved.

The description of the different illustrative embodiments has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different illustrativeembodiments may provide different features as compared to otherdesirable embodiments. The embodiment or embodiments selected are chosenand described in order to best explain the principles of theembodiments, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various embodimentswith various modifications as are suited to the particular usecontemplated.

What is claimed is:
 1. A method of determining a property of a fluid ina vessel, comprising: applying a first magnetic field to the fluid inthe vessel from outside of the vessel to rotationally align magneticdipole particles in the fluid; stopping applying the first magneticfield to the fluid in the vessel when the magnetic dipole particles inthe fluid are rotationally aligned; after stopping applying the firstmagnetic field, detecting a second magnetic field from outside of thevessel, wherein the second magnetic field is generated by the magneticdipole particles in the fluid; and determining the property of the fluidin the vessel from the second magnetic field.
 2. The method of claim 1,wherein determining the property of the fluid in the vessel comprisesdetermining a vorticity or a velocity of flow of the fluid in thevessel.
 3. The method of claim 1, wherein determining the property ofthe fluid in the vessel comprises determining a temperature of the fluidin the vessel.
 4. The method of claim 1, wherein determining theproperty of the fluid in the vessel comprises determining a state ofstress or strain of the fluid in the vessel.
 5. The method of claim 1,wherein the fluid is optically opaque and magnetically transparent. 6.The method of claim 1, wherein the vessel is optically opaque andmagnetically transparent.
 7. The method of claim 1, further comprisingplacing the magnetic dipole particles in the fluid in the vessel.
 8. Amethod of determining a property of a fluid in a vessel, comprising:applying a first magnetic field to the fluid in the vessel from outsideof the vessel to rotationally align magnetic dipole particles in thefluid; stopping applying the first magnetic field to the fluid in thevessel when the magnetic dipole particles in the fluid are rotationallyaligned; after stopping applying the first magnetic field, detecting asecond magnetic field outside of the vessel, wherein the second magneticfield is generated by the magnetic dipole particles in the fluid;determining a flow of fluid in the vessel from the second magneticfield; and displaying a graphical representation of the flow of fluid inthe vessel.
 9. The method of claim 8, wherein the vessel is opticallyopaque and magnetically transparent.
 10. The method of claim 8, whereinapplying the first magnetic field comprises applying the first magneticfield using a Helmholtz coil.
 11. The method of claim 8, whereindetecting the second magnetic field comprises detecting the secondmagnetic field using magnetometers or giant magneto-resistive sensors.12. The method of claim 8, wherein determining the flow of fluid in thevessel comprises inverting magnetic field measurements of the secondmagnetic field using a particle field model to determine movement of themagnetic dipole particles in the vessel.
 13. The method of claim 8,wherein displaying the graphical representation of the flow of fluid inthe vessel comprises displaying a three-dimensional time-varying map ofpaths of movement of the magnetic dipole particles.
 14. The method ofclaim 8 further comprising placing the magnetic dipole particles in thefluid in the vessel.
 15. An apparatus, comprising: a magnetic fieldgenerator; a magnetic field generator controller configured to controlthe magnetic field generator to apply a first magnetic field to a fluidin a vessel from outside of the vessel to rotationally align magneticdipole particles in the fluid and to stop applying the first magneticfield to the fluid in the vessel when the magnetic dipole particles inthe fluid are rotationally aligned; a magnetic field sensor configuredto detect a second magnetic field outside of the vessel, wherein thesecond magnetic field is generated by the magnetic dipole particles inthe fluid after applying the first magnetic field to the fluid in thevessel is stopped; a fluid flow calculator configured to determine aflow of the fluid in the vessel from the second magnetic field; and adisplay generator configured to generate a graphical representation ofthe flow of fluid in the vessel.
 16. The apparatus of claim 15, whereinthe vessel is optically opaque and magnetically transparent.
 17. Theapparatus of claim 15, wherein the magnetic field generator comprises aHelmholtz coil.
 18. The apparatus of claim 15, wherein the magneticfield sensor comprises giant magneto-resistive sensors or magnetometers.19. The apparatus of claim 15, wherein the fluid flow calculator isconfigured to determine the flow of fluid in the vessel by invertingmagnetic field measurements of the second magnetic field using aparticle field model to determine movement of the magnetic dipoleparticles in the vessel.
 20. The apparatus of claim 15, wherein thedisplay generator is configured to generate the graphical representationof the flow of fluid in the vessel comprising a three-dimensionaltime-varying map of paths of movement of the magnetic dipole particles.